I just enlisted into the Army Reserves on December 18, 2019. I haven't received basic training or receive any military pay. Should I list my enlistment on 2019's returns?

No!!  Do not enter any enlistment information on your return unless you receive a W2 or any other tax document for 2019. More than likely, any income will be reported on your 2020 return

That's what I thought. Thank you for your timely response.